On 05/31/2016 07:24 PM, Tom Lane wrote:
Tomas Vondra <tomas.von...@2ndquadrant.com> writes:
On 05/31/2016 06:59 PM, Tom Lane wrote:
I'm confused here --- are you speaking of having removed
        if (msg->cutoff_time > req->request_time)
                req->request_time = msg->cutoff_time;
? That is not a check for clock skew, it's intending to be sure that
req->request_time reflects the latest request for this DB when we've
seen more than one request. But since req->request_time isn't
actually being used anywhere, it's useless code.

Ah, you're right. I've made the mistake of writing the e-mail before
drinking any coffee today, and I got distracted by the comment change.

I reformatted the actual check for clock skew, but I do not think I
changed its behavior.

I'm not sure it does not change the behavior, though. request_time only
became unused after you removed the two places that set the value (one
of them in the clock skew check).

Well, it's unused in the sense that the if-test quoted above is the only
place in HEAD that examines the value of request_time.  And since that
if-test only controls whether we change the value, and not whether we
proceed to make the clock skew check, I don't see how it's related
to clock skew or indeed anything else at all.

I see, in that case it indeed is useless.

I've checked how this worked in 9.2 (before the 9.3 patch that split the file per db), and back then last_statsrequest (transformed to request_time) was used to decide whether we need to write something. But now we do that by simply checking whether the list is empty.


Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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